The present invention relates to the field of drive mechanisms for transporting photosensitive film or paper to and from the exposure platen of a phototypesetter or the like.
In transporting photosensitive paper into the exposure station of a phototypesetter, it is important to provide balanced driving forces to prevent the feed direction of the paper from becoming skewed relative to the center line of the drive mechanism.
In a prior design, four drive rollers were mounted upon a drive shaft and were in contact with four pinch rollers and pressure adjustment springs, positioned about a central support bearing, were employed. With this unit, it was difficult to obtain balanced bite pressures at the roller interfaces as changes in the bite pressure of one roller pair, would affect the pressures of other pairs, such variations of pressure being caused by, for example, lack of concentricity of the rollers. In accordance with the present design, means are provided to widely separate the rollers in order to readily clear paper jams, clean rollers, and prevent the rollers from being flattened due to setting, when the machine is not being operated, and independent suspension of one roller of each roller pair is effected. Thus the bite pressure of each roller pair may be individually adjusted in accordance with a spring/set screw arrangement, without altering the bite pressures of other roller pairs.
It is thus an object of the present invention to provide a relatively simple mechanism for individually adjusting the bite pressures between four pair of drive rollers, and yet allow rapid and easy roller separation for the purposes setforth above.
It is a further object of the present invention to provide a mechanism for performing the above stated function which utilizes the same individually adjusted bite pressure springs to also lock and unlock the separation mechanism.